Synthesis of Pd nanorod arrays on Au nanoframes for excellent ethanol electrooxidation.

Au-Pd hollow nanostructures have attracted a lot of attention because of their excellent ethanol electrooxidation performance. Herein, we report a facile preparation of Au nanoframe@Pd array electrocatalysts in the presence of cetylpyridinium chloride. The reduced Pd atoms were directed to mainly deposit on the surface of the Au nanoframes in the form of rods, leading to the formation of Au nanoframe@Pd arrays with a super-large specific surface area. The red shift and damping of the plasmon peak were ascribed to the deposition of the Pd arrays on the surface of the Au nanoframes and nanobipyramids, which was verified by electrodynamic simulations. Surfactants, temperature and reaction time determine the growth process and thereby the architecture of the obtained Au-Pd hollow nanostructures. Compared with the Au nanoframe@Pd nanostructures and Au nanobipyramid@Pd arrays, the Au nanoframe@Pd arrays exhibit an enhanced electrocatalytic performance towards ethanol electrooxidation due to an abundance of catalytic active sites. The Au NF@Pd arrays display 4.1 times higher specific activity and 13.7 times higher mass activity than the commercial Pd/C electrocatalyst. Moreover, the nanostructure shows improved stability towards the ethanol oxidation reaction. This study enriches the manufacturing technology to increase the active sites of noble metal nanocatalysts and promotes the development of direct ethanol fuel cells.

A novel deposition mechanism of Au on Ag nanostructures involving galvanic replacement and reduction reactions.

Combining a galvanic replacement reaction with a reduction reaction can provide more possibility in the synthesis of Au-Ag hollow nanostructures. However, the detailed atomic deposition mechanism involving these two reactions is unclear. Herein, we proposed a novel deposition mechanism of the Au atoms on Ag nanostructures involving simultaneous galvanic replacement and reduction reactions. The Au atoms originating from galvanic replacement reaction will deposit at surface energy-related facets of the Ag nanostructures while the others originated from reduction reaction at high curvature sites, with the morphology of the final Ag@Au nanostructures determined by the ratio between the two reactions. This mechanism has been verified by experiments on Ag nanorods using varied volumes of Au precursor. Moreover, it can also be extended to Ag cuboctahedrons, suggesting the generality of this mechanism.

Au nanobipyramids with Pt decoration enveloped in TiO2 nanoboxes for photocatalytic reactions.

Noble metal nanocrystals and core-shell nanocomposites have attracted particular interest due to their unique optical properties originating from surface plasmon resonance (SPR) and wide applications related to the SPR effect. In this work, we designed and fabricated a new Au-Pt@TiO2 nanocomposite, in which Au nanobipyramids (AuNBPs) decorated with platinum (Pt) clusters were enveloped in mesoporous TiO2 nanoboxes with nanocavities. AuNBPs provide strong SPR absorption and localized field enhancement restricted to the cavities of TiO2 nanoboxes. The Pt nanoclusters decorated on the surface of AuNBPs can effectively modulate the charge movement and energy transfer in the photocatalytic process. The enhanced electric field provides a local thermal effect for the photocatalytic reaction and promotes the injection process of hot electrons which facilitates carrier separation. The nanoboxes with nanocavities can effectively manage the usage of localized energy and provide space for reaction. Under the cooperative effects, the photocatalytic performance was remarkably improved along with durability and stability. For the AuNBP-Pt@TiO2 nanoboxes, the rhodamine-B degradation efficiency was ∼6.5 times that of AuNBP@TiO2 nanoboxes. The mechanism of the photocatalysis process was proposed based on experimental results and simulations. Benefiting from the excellent structure and properties, the obtained nanostructure is a promising candidate in the fields of pollutant degradation and chemical reaction catalysis.

Gold nanobipyramid-embedded silver-platinum hollow nanostructures for monitoring stepwise reduction and oxidation reactions.

Metal hollow nanostructures based on gold nanobipyramids (Au NBPs) are of great interest for the combination of tunable plasmonic resonances and excellent physicochemical properties. Based on the core-shell Au NBP@Ag nanorods with desired sizes, herein we reported the synthesis and growth mechanism of Au NBP-embedded AgPt hollow nanostructures with tunable thickness and size. The Au NBP@AgPt nanoframes were obtained at lower temperature, in which cetyltrimethylammonium bromine (CTAB) was applied as a capping agent to guide the deposition of Pt atoms on the edges and corners of Au NBPs@Ag nanorods. With the increase of reaction temperature, the Au NBP@AgPt nanoframes convert into nanocages due to the atomic migration to the surfaces. The surface plasmon resonance of the Au NBP@AgPt hollow nanostructure shifts from red to blue, which is ascribed to the changes in coverage area and location site of the AgPt alloy. When CTAB was replaced by cetyltrimethylammonium chloride (CTAC), Au NBP@AgPt nanocages dominate the product. The surface roughness and thickness of the nanocages can be controlled by the temperature and the amount of Pt precursor. Moreover, Au NBP@AgPt hollow nanostructures show excellent surface-enhanced Raman scattering and exhibit remarkable stability in harsh environments. Taking into account the advantages of the plasmonic property (Au NBPs), catalytic activity (Pt) and plasmon-enhanced signal (Ag), the Au NBP@AgPt hollow nanostructures are a promising candidate for technological applications in catalytic reactions.